The present invention relates to automatic or semi-automatic systems or devices for transmitting torque through the power trains of a motor vehicles that are equipped with an engine, a transmission with a plurality of transfer ratios, and a clutch which in the preferred case establishes a torque-transmitting connection between the engine and the transmission, but could also be arranged downstream of the transmission.
The transmission system preferably includes automatic clutch-actuator means to control the state of engagement of the clutch. It can also be advantageous if the system includes automatic transmission-actuating means to control the operating state of the transmission.
In transmission systems of this kind, the engine is started preferably with the clutch in a disengaged condition. Through a subsequent movement of a shifter element such as a selector lever, a gear is engaged through a control unit and the transmission-actuating means, and the clutch is moved into engagement, e.g., by depressing the accelerator pedal and/or increasing the engine rpm rate.
Existing systems that work in this manner have some undesirable traits, e.g., if the vehicle is parked on an incline and secured only by an engaged gear without using the parking brake. In this situation, the vehicle can roll away when the clutch is disengaged to start the engine, which can take the driver by surprise.
As described in the earlier patent application WO 94/05522, the clutch disengagement and engine start are blocked in systems of this kind, if a gear is found to be engaged when switching on the ignition. The clutch and the engaged gear can be disengaged by moving the shifter element into the neutral position. As an alternative, the system can be equipped with separate means to prevent starting the engine if the transmission is not in a neutral position. In this case, the transmission has to be shifted into neutral before the engine can be started.
The foregoing arrangement is acceptable if the shifter element has to be moved intentionally by the driver, so that the driver anticipates that the clutch will be uncoupled and the gear will be disengaged. However, the system also allows the gear-shifting lever to be moved to the neutral position after the ignition has been turned off. It is desirable in this case if the clutch remains engaged and transmission stays in gear, rather than moving out of engagement when the system is activated again.
It is therefore the object of the present invention to provide a transmission system for a motor vehicle with safeguards, so that the vehicle will not start moving unintentionally and/or unsafely.
To meet the foregoing objective, the present invention provides a transmission system for a motor vehicle that is equipped with an engine, a transmission with a plurality of transfer ratios, and a clutch which in the preferred case establishes a torque-transmitting connection between the engine and the transmission, but could also be arranged downstream of the transmission. The transmission system has clutch-actuator means to control the state of engagement of the clutch, and transmission-actuating means to shift the transmission into and out of the different gears. Gear-monitoring means are provided to determine if a gear is engaged. There are also means provided to block disengagement of the clutch and shifting of the transmission into neutral for the purpose of starting the engine if upon activating the system, the gear-monitoring means indicate that a gear is engaged. The transmission system of the present invention is equipped with a clutch-disengaging means that allows the clutch to disengage if the transmission is in gear at the time the system is switched on, under the condition that the main brake of the vehicle is applied and the applied state of the main brake is confirmed, or if the shifter element is in a gear position and is moved to the neutral position subsequent to activating the transmission system.
If the vehicle is parked with the transmission in gear, the clutch is taken out of engagement according to the invention, if the main brake of the vehicle is applied so that the vehicle will not start to move unintentionally, or if the driver takes specific action to move the shifter element to the neutral position.
According to a preferred embodiment of the invention, a main-brake sensor, e.g., a brake switch, is used to verify that the main brake is applied. However, the main-brake sensor may not be absolutely reliable. Consequently, additional means are required to ensure that a failure of the main-brake sensor will not lead to one of the following:
an erroneous indication that the main brake is applied, which would inappropriately cause the clutch to be taken out of engagement, or
an erroneous indication that the main brake is not applied, which would inappropriately cause the clutch to be blocked.
To prevent the foregoing malfunctions, the invention preferably provides means for monitoring the reliability of the main-brake sensor.
In addition, the invention provides a means whereby the blocking of the clutch disengagement is canceled in situations where the reliability of the main-brake sensor is questionable.
The novel features that are considered as characteristic of the invention are set forth in particular in the appended claims. The improved apparatus itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawing.